In Vermont, a riotous part of N America (7)
I believe the answer is:
ontario
'part of n america' is the definition.
(I've seen this before)
'in vermont a riotous' is the wordplay.
'in' says the answer is hidden in the clue.
'ONTARIO' is hidden in the letters of 'vermont a riotous'.
(Other definitions for ontario that I've seen before include "Canadian Great lakes province" , "part of Canada" , "A North American lake" , "part of N America" , "Root in a Great Lake" .)